Synthetic resins are widely used as engineering plastics in a variety of end-uses, such as building materials and automobile parts. The engineering resins have good physical and chemical resistance, and are low cost. A disadvantage of some engineering resins is that they have poor impact strength. Poor impact strength of these materials may be overcome by blending impact modifiers with the resins.
Impact modifiers generally consist of low-Tg, elastomeric polymers. Unfortunately the low-Tg polymer particles are typically difficult to handle. They are tacky and tend to stick together (blockiness), forming clumps or agglomerates during processing and storage. The agglomerates may be difficult to separate and disperse into the engineering polymer matrix, leading to a less than optimal modification of the plastic.
Core shell impact modifiers typically have rigid high Tg polymers in their outmost shell at levels sufficient to cover the elastomeric components. Such impact modifiers have good anti-blocking properties and are easy to handle. They can also be spray-dried or coagulated.
Hydroxy alkyl (meth)acrylate monomers have been incorporated into the shell of a core-shell modifier to improve compatiblization of the shell with the matrix polymer. The use of hydroxy-functional monomers in the shell has been described in U.S. Pat. Nos. 5,321,056 and 5,409,967.
JP 54-48850 describes the use of polymers made from hydroxyl-functional monomers for use as impact modifiers.
U.S. Pat. No. 6,130,290 describes a core-shell particle having a two-part shell. The outer shell contains a hydroxy alkyl (meth)acrylate copolymer, while the inner shell does not.
U.S. Pat. No. 7,195,820 describes a core-shell polymer impact modifier with hydrophilic monomer units in the shell. The purpose of the hydrophilic shell monomers units was to resist migration of the shell polymer into the core—thus reducing the amount of polymer shell needed for complete coverage of the core. These core-shell impact modifiers were considered useful in many different polymer matrixes.
Polymer matrixes consisting of blends of functional polymers with non-functional materials present a unique challenge for impact modification. Conventional core-shell impact modifiers with non-functional shells tend to migrate toward the non-functional parts of the blend. This decreases the effectiveness of the impact modifier on the functional polymer.
In “Functional MBS Impact Modifiers for PC/PBT Alloy” by William T. W. Tseng, and J. S. Lee, Journal of Applied Polymer Science, Vol. 76, 1280-1282 (2000) the use of a functionalized MBS in a PC/PBT is explored. A PC/PET blend was not described. Applicants have found a much greater synergy for a functionalized MBS in a PC/PET alloy, than in a PC/PBT alloy.
Surprisingly it has been found that the impact modification properties of functional and non-functional resin alloys can be improved by using an impact modifier having a functionalized shell. One system showing an especially large impact improvement from the functional MBS impact modified is a polycarbonate/polyethylene terephthalate alloy.
While not being bound by any particular theory, it is believed that the functionalization in the particle shell associates with the functionalized polymer in the matrix, thus preventing migration of much of the core-shell impact modifier into the non-functionalized portions of the matrix, and providing localized dispersion. In a PET blend, the hydroxyl functionality on the PET reacts with the functional group on the functionalized MBS, anchoring much of the MBS in the brittle PET phase. Additionally, the use of a functionalized shell decreases the migration of shell monomer into the core during polymerization of the core-shell polymer, providing better shell coverage.